On 18.10.23 01:46, David Woodhouse wrote:
From: David Woodhouse <dwmw@xxxxxxxxxxxx> The xencons_connect_backend() function allocates a local interdomain event channel with xenbus_alloc_evtchn(), then calls bind_interdomain_evtchn_to_irq_lateeoi() to bind to that port# on the *remote* domain. That doesn't work very well: (qemu) device_add xen-console,id=con1,chardev=pty0 [ 44.323872] xenconsole console-1: 2 xenbus_dev_probe on device/console/1 [ 44.323995] xenconsole: probe of console-1 failed with error -2 Fix it to use bind_evtchn_to_irq_lateeoi(), which does the right thing by just binding that *local* event channel to an irq. The backend will do the interdomain binding. This didn't affect the primary console because the setup for that is special — the toolstack allocates the guest event channel and the guest discovers it with HVMOP_get_param. Once that's fixed, there's also a warning on hot-unplug because xencons_disconnect_backend() unconditionally calls free_irq() via unbind_from_irqhandler(): (qemu) device_del con1 [ 32.050919] ------------[ cut here ]------------ [ 32.050942] Trying to free already-free IRQ 33 [ 32.050990] WARNING: CPU: 0 PID: 51 at kernel/irq/manage.c:1895 __free_irq+0x1d4/0x330 Fix that by calling notifier_del_irq() first, which only calls free_irq() if the irq was requested in the first place. Then use
I don't think the "if the irq was requested in the first place" is the correct reasoning. I think the problem is that notifier_del_irq() will be called another time through the .notifier_del hook. Two calls of notifier_del_irq() are fine, but one call of it and another call of free_irq() via unbind_from_irqhandler() is a problem.
evtchn_put() to release the irq and event channel. Avoid calling
xenbus_free_evtchn() in the normal case, as evtchn_put() will do that
too. The only time xenbus_free_evtchn() needs to be called is for the
cleanup when bind_evtchn_to_irq_lateeoi() fails.
Finally, fix the error path in xen_hvc_init() when there's no primary
console. It should still register the frontend driver, as there may be
secondary consoles. (Qemu can always add secondary consoles, but only
the toolstack can add the primary because it's special.)
Fixes: fe415186b4 ("xen/console: harden hvc_xen against event channel storms")
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
With above fixed in the commit message: Reviewed-by: Juergen Gross <jgross@xxxxxxxx> Juergen
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